This occurs when a client has previously registered with another coach first (more often than not, this would be on the main Health Coach Group site). The system recognizes who they first registered with when sending out the emails.
To remedy this, simply log into the admin/site owner’s account, hover over the name on the top right of the page, and select Edit My Profile. Then select the button at the bottom of the page to update the profile (no actual changes need to be made to the profile). Click that button and the issue is remedied.